<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <script>
      var reg;
      window.onmessage = function (event) {
        if (event.data !== "register") {
          return;
        }
        var promise = navigator.serviceWorker.register("worker.js");
        window.onmessage = function (event) {
          if (event.data === "register") {
            promise.then(function (registration) {
              return navigator.serviceWorker.register("worker2.js")
                .then(function(registration) {
                  reg = registration;
                });
            });
          } else if (event.data === "unregister") {
            reg.unregister();
          }
        };
      };
    </script>
  </head>
  <body>
    This is a test page.
  </body>
<html>
